Hammer pistons and tools provided therewith



Nova. 12, 1957 H, T, PYK 2,812,745

HAMMER PISTONS AND TOOLS PROVIDED THEREWITH Filed Feb. 19, 1952 4Sheets-Sheet 1.

gunman) Nov. 12, 1957 H. r. PYK 2,812,745

HAMMER PISTONS AND TOOLS PROVIDED THEREWITH Filed Feb. 19, 1952 4Sheets-Sheet 2 D Nub vii, 1 957 I TDPYK 2,812 745 HAMMER PISTONS ANDTOOLS PROVIDED THEREWITH I Filed Feb. 19. 1952 4 Sheets-Sheet 3 Fig.3

Nqv. 12, 1957 H. 'r. PYK 2,812,745

I HAMMER PISTONS AND TOOLS PROVIDED THEREWITH Filed Feb. 19. 1952 I 4Sheets -Sheet 4 Fig.5

HAMMER PISTONS AND TOOLS PROVIDED THEREWITH Herman Theodor Pyk,Saltsjo-Duvnas, Sweden, assignor to Atlas Copco Aktiebolag, acorporation of Sweden Application February 19, 1952, Serial No. 272,475

Claims priority, application SwedenFebmary 20, 1951 11 Claims. (Cl.121-31) This invention relates to freely reciprocable hammer pistons forpercussion tools driven by an elastic pressure fluid and to percussiontools provided with such hammer pistons. One object of the invention isto provide an improved hammer piston forsuch tools which permits thetransmission of a greater quantity of energy at each blow to a workingimplement, such as a rock drill rod, a chisel, a riveting tool, or thelike, than in hammer pistons of conventional design without increasingthe maximum stresses in the working implement. This may be obtained bythe provision of a hammer piston which without increasing the amplitudeof the percussion wave produced in the impact receiving member increasesthe length of the wave or the duration of the maximum amplitude of thewave. A further object of the invention is to provide hammer pistons forrock drills which may be made to suit various kinds of rock and toproduce various shapes of the percussion wave to suit the differentkinds of rock for producing the most favourable drilling result. A stillfurther object of the invention is to provide a hammer piston theelastic properties of which are adjustable. The expression elasticflexing used in the following specification and. claims is intended toindicate such a flexing in a body or a material which does not produce apermanent change of the shape of the body or the material. For the aboveand other purposes I provide a freely reciprocablehammer piston forpercussion tools driven by an elastic pressure fluid and having a pistonhead and an impact portion so constructed that a substantial portion ofthe mass of the piston head will flex elastically in the direction ofthe blows relative to the rest of the piston in such a manner that upondelivery of a blow to a member by the impact portion an elastic flexingof the above mentioned substantial portion of the mass of the pistonhead in the direction of the blow is obtained which is materiallygreater than the elastic flexing of a solid cylindrical steel pistonwith the same weight and length as the hammer piston upon an equivalentimpact but which does not exceed the flexing of a solid cylindricalsteel piston with the same weight and ten times the length of the hammerpiston upon an equivalent impact. Preferably the main portion of themass of the piston head is designed to-flex elastically in the directionof the blows. Such a head may comprise a plurality of superimposedelastic elements capable of flexing in the direction of the blowrelative to the impact delivering portion of the piston. The inventionalso includes percussion tools provided with hammer pistons according tothe invention and with means for imparting a reciprocating motion to thehammer piston withthe aid of an elastic pressure fluid, such ascompressed air pressure gas, or the like.

In the accompanying drawings some embodiments of hammer pistonsandhammer tools according to the invention are illustrated by way ofexample. Fig. 1. is a side elevation and partial section of a compressedair driven hammer rock drill according to the invention and proyidedwith a differential hammer piston. Fig. 2 is a side nited States Patent9 i 2,812,745 Patented Nov. 12, 1957 elevation and partial section of acompressed air driven concrete breaker provided with a hammer pistonaccording to the invention. Figs. 3 and 4 illustrate on a larger scaleand partially in section the hammer pistons of the percusson toolsaccording to Figs. 1 and 2, respectively. Figs. 5 and 6 illustratehammer pistons according to two further embodiments of theinvention.

The compressed air driven hammer rock drill illustrated in Fig. 1consists of a cylinder 1, a back head 2, a valve casing 3, a front head4, and an intermediate casing 5. The back head 2 andthe valve casing 3form together a valve chamber 6, in which a valve member controlling thedistribution of compressed air for producing the working stroke and thereturn stroke, respectively, of the hammer piston is arranged inconventional manner. In the embodiment illustrated in Fig. 1 the valvemember comprises an oscillating disc valve 7 but the invention isobviously not confined to the. use .of such a valve and a drillaccording to the invention may, for instance, be provided with tubularvalves, disc valves, piston valves, double valves, or other conventionalvalve designs suitable for controlling the distribution of compressedair to the working cylinder and in some case the exhaust of the air fromthe working cylinder of the drill.

The front head 4 of the drill and the intermediate casing 5 enclose adrill turning mechanism which may be of any conventional design andwhich in the illustrated embodiment consists of a motor 8 which drives ashaft 9 carrying a screw which engages a worm wheel 10 formed on a drillchuck 11 in which a drill rod 12 is fitted. 13 is the main admissionvalve of the drill which controls the supply of compressed air to thevalve chamber 6 and the turning motor 8, and 14 is a handle secured atthe back head of the drill. 15 indicates a connection for supplyingflushing water to the drill.

The cylinder 1 contains a reciprocable hammer piston which isillustrated in detail in Fig. 3 and which consists of a steel portion 16designed for delivering impacts directly to a drilling implement and ofcylindrical shape of reduced diameter and a piston head of largerdiameter comprising a plurality of elastically flexing steel discs 17.The impact portion 16 is provided with a duct 18 for accommodating awater flushing tube 19 and is movable and guided nad forms a seal in amember 29 forming the lower head of the working chamber of thecylinder 1. The portion 16 has a further reduced extension 21 whichextends through the piston head and on which the discs 17 arefitted andsecured in position by a nut 22. The discs 1'7 together in effect form astiff spring the tension of which may be adjusted by tightening orloosening the nut 22. The adjustment of the tension or the flexingability of the discs is made possible by the discs having one surfaceconvex, as indicated at 23, and the opposite surface provided with aperipheral ridge 24. The discs 17 are superimposed in such a manner thatthey contact each other alternately at the two convex faces 23 and thetwo ridges 24, as clearly shown in Fig. 3.

Upon suitable tightening of the nut 22 the discs contact each other atthe ridges 24 and along circles having a diameter larger than thediameter of the extension 21. The total flexing in the direction of ablow of such a piston of a suitable material usch as flexible steel andof suitable thickness of the discs and with a length L is materiallylarger than the elastic flexing in the direction of a blow of a solidcylindrical steel piston 25 of circular cross section and the sameWeight and length L as the hammer piston described above. Preferably theelastic flexing may be over 20% larger than that of the solid steelpiston 25. This means, for instance, that if the cylindrical solidpiston 25 is subjected to a load P and a reduction of the lengthresulting therefrom is AL then the compression of the piston 16, 17according to theinvention r 3 when the upper disc is subjected to thesame load P would be more than 1.2 AL.

If the nut 22 is tightened less a piston is obtained in which the totalflexing in the direction of the blow is larger than above described.This means that if such a piston is subjected to a load P this loadwould produce a compression, for instance of the order of 1.5AL. Thismeans that the discs 17 apart from contacting each other along theridges 24 contact each other along circles with a diameter closer to thediameter 21 than in the first case.

By making the discs 17 of less thickness or of larger diameter thanillustrated in Fig. 3 the piston head may be made still weaker so thatthe flexing at a certain load P is for instance more than 2AL, i. c.more than 160% larger than the elastic compression of the comparablesolid piston 25 subjected to the same load.

During the operation of the above described hammer piston in apercussion tool it may be assumed that the piston acts as if the pistonhead was made of a solid material having a lower modulus of elasticitythan the steel in the comparable solid steel piston 25.

However, the elasticity of the hammer piston according to the inventionshould not be too great and under no circumstances should the hammerpiston be so weak that upon an impact it will flex more than acylindrical solid steel piston with the same weight as the hammer pistonand ten times its length. Preferably the hammer piston should not flexmore than a cylindrical solid steel piston of the same Weight as thehammer piston and with the same diameter as the working implement towhich the hammer piston is designed to deliver impacts.

The concrete breaker illustrated in Fig. 2 consists of a cylinder 26, aback head 27 provided with a handle and an admission valve, a front head23 carrying a retainer 29 for a tool 3%, and an intermediate portion 31forming the front head of the working cylinder. An anvil block 32 ismounted in the intermediate portion 31 and serves to transmit percussionenergy from the hammer piston to the tool 30 and to provide a seal inthe front head of the working cylinder.

The hammer piston cf the concrete breaker in Pig. 2 which is illustratedon a larger scale in Fig. 4 consists of a central rod forming an impactportion 33 and carrying a plurality of flexible steel discs 34 fitted onthe rod and maintained thereon by a nut 35. The discs 34 are provided attheir outer periphery with a peripheral ridge 36 and at their innerperiphery with a peripheral ridge 37. The discs contact each otheralternately at the ridges 36 and 37 so that a very stiff bellows typespring is formed by the discs. A hammer piston according to thisembodiment has a flexibility in the direction of the blows which issubstantially greater than the flexibility of a solid cylindrical steelpiston of circular cross section and of the same weight and length asthe hammer piston but should such flexibility, according to theinvention, not be greater than the flexibility of a solid cylindricalsteel piston of circular cross section and of the same weight and tentimes the length of the hammer piston. A weak flexible piston of thistype produces a rather elongated percussion wave.

Fig. illustrates a hammer piston of a rock drill which is a modificationof Figs. 1 and 3. The impact portion 38 according to Fig. 5 is providedwith straight and oblique grooves 39, 4t) in order to rovide means forobtain ing the drill bit by virtue of power taken from the piston in aconventional manner (not illustrated). The piston head consists of acylindrical sleeve 41. in which a stiff bellows type spring forming themain part of the mass of the piston head is disposed between the base 42of the sleeve and a disc-shaped flange 43 at the upper end of the impactportion 38. The spring may be compressed by means of a disc 44screw-threaded into the open end of the sleeve 41 and enclosing thedisc-shaped flange 43. The spring consists of annular bellows elements 5comprising two steel discs connected at their inner peripheral edges soas to form integral elements provided with outer peripheral ridges 46 bymeans of which the elements contact each other, the base 42 of thesleeve and the flange 43 so as to form a stiff bellows type spring. Thisstructure is fitted and guided on a central extension 52 of the impactportion 38.

Fig. 6 illustrates a piston in which the main part of the mass of thepiston head is made of a material having other elastic properties thansteel. The piston consists of an impact portion 47 carried at the end ofa rod 48 provided with a flange 49 and a nut 56 between which and theflange a tubular cylindrical body 51 is secured. This body may be madeof bronze or other material with at least a 30% lower modulus ofelasticity than steel so that said body is capable of flexing in thedirection of the blows substantially more than a steel piston of thesame length and weight. In order that this body shall not be too lightthe material of the body 51 should preferably have a specific gravity ofmore than 4 kilogrammes pc cubic decimetre.

The above described embodiments of the invention should be consideredonly as examples and the invention may be modified in several differentways within the scope of the claims. The piston or the piston head may,for instance, be made as an integral bellows type spring in which casethe discs 17, 34 or elements 45 are connected at their inner and outeredges. The central rod 21, 33, 46, 48 may be dispensed with if theflexible piston head itself 'is constructed to form an impact portion.Preferably, a piston according to the invention may be designed todeliver blows with an impact velocity of more than 5 metres per second.

What I claim is:

l. A free motion hammer piston for percussion tools driven by an elasticpressure fluid comprising a piston head acted on by the pressure fluidto reciprocate the piston, a portion designed for delivering impacts toa member, a plurality of elements forming the major portion of the massof said head and having a specific gravity greater than 4 and arrangedin such a manner that they are in part axially spaced to permit thespaced parts to flex axially in the direction of the blows upon animpact of said impact portion on said member.

2. A hammer piston according to claim 1 in which the flexible elementscomprise flexible discs superimposed in the direction of the blows withthe spaced parts of the discs arranged to permit flexing of the discs inthe direction of the blows relative to the rest of the piston.

3. A free motion hammer piston for percussion tools comprising a pistonhead, a portion designed for delivering impacts, a plurality of flexiblediscs formed as separate elements contacting each other alternately atinner and outer edges so as to form a flexible bellows structure formingthe major portion of the mass of said head, and means for holding saiddiscs and said impact portion together.

4. A hammer piston according to claim 3 in which at least certain of theflexible discs provide confronting surfaces of revolution contactingeach other along circles the radius of which is variable in accordancewith the pressure exerted on said discs.

5. A hammer piston according to claim 3 in which said means isadjustable to produce an initial stress in the flexible portion of saidpiston head.

6. A free motion hammer piston for percussion tools comprising a pistonhead, a portion designed for delivering impacts, and an integralflexible bellows capable of flexing elastically in the direction ofblows and forming the major portion of the mass of said head.

7. A free motion hammer piston for percussion tools comprising a pistonhead, a portion designed for delivering impacts, a plurality of flexiblebellows elements, each element comprising at least two discs connectedto each other to'form integral bodies, and means for holding saidbellows elements and said impact portion together.

8. A hammer piston according to claim 7 in which said means isadjustable to produce an initial stress in the flex ible portion of saidpiston head.

9. A hammer piston for percussion tools in which said hammer piston isreciprocated by means of an elastic pressure fluid and comprising animpact delivering piston portion, and a piston head the major portion ofthe mass of which comprises a plurality of elastic elements with aspecific gravity greater than 4 in superimposed arrangement and in partaxially spaced so as to permit the spaced parts of said elements to flexelastically in the direction of movement of the piston relative to saidimpact delivering portion when the impact delivering portion is arrestedat the end of a working stroke of the piston.

10. A hammer piston for percussion tools in which said hammer piston isreciprocated by means of an elastic pressure fluid and comprising animpact delivering piston portion, a metallic piston head the major massof which forms a spring, and means for adjustably compressing saidspring in the direction of movement of said piston.

11. In a percussion tool having a working cylinder, a hammer pistonreciprocable in said cylinder, means for supplying elastic pressurefluid to said cylinder to reciprocate said piston, said pistoncomprising a first portion adapted to deliver impact blows directly to ablowreceiving member and a second portion forming a piston head themajor portion of the mass of which comprises a plurality of elasticelements with a specific gravity greater than 4 in superimposedarrangement and in part axially spaced so as to permit the spaced partsof said elements to flex elastically in the direction of movement of theimpact delivering portion of the piston in said impact deliveringdirection when said first portion of the piston is arrested at the endof a working stroke of the piston.

References Cited in the file of this patent UNITED STATES PATENTS618,324 Blum Jan. 24, 1899 1,105,876 Briegel Aug. 4, 1914 1,884,969Carpenter Oct. 25, 1932 2,025,288 Johnson Dec. 24, 1935 FOREIGN PATENTS283,849 Great Britain July 12, 1928 322,515 Great Britain Dec. 5, 1929536,880 Germany 1931 984,182 France 1951

